The present invention relates to a lighting device that uses a plurality of solid-state light emitting elements as a light source and as applied to an illumination fixture.
Lighting devices are known in which a plurality of solid-state light emitting elements are mounted on a board. In general, the plurality of solid-state light emitting elements may be light-emitting diodes (hereinafter referred to as LEDs) that emit blue light. In this sort of lighting device, the plurality of LEDs mounted on the board are individually sealed by a translucent resin layer and covered by a wavelength converting member. The wavelength converting member contains phosphors that convert the blue light emitted from the plurality of LEDs to, for example, yellow light. Based on this, when the blue light is irradiated on the phosphors, the yellow light is emitted from the phosphors. The blue light not irradiated on the phosphors and the yellow light are accordingly combined and emitted as white light from a surface of the wavelength converting member.
Typically, in the lighting device, the solid-state light emitting elements are uniformly distributed. However, the phosphors in the solid-state light emitting elements are not necessarily uniform, and therefore color unevenness occurs as a whole. Also, a light emitting portion of the solid-state light emitting element is relatively small in size, and therefore luminance of the light emitting part is increased and results in a degree of undesirable glare.
A lighting device as previously known in the art may address these problems by leading out light through a fluorescent substance layer and a diffusion layer that are provided in common, separate from a solid-state light emitting element array. However, such a lighting device has two problems described below.
First, although the fluorescent substance layer is arranged separately from the solid-state light emitting elements, a sealing member is in close contact with the fluorescent substance layer through an adhesive layer, so that emission light from the solid-state light emitting elements is directly incident on the fluorescent substance layer, and an incident density on the fluorescent substance layer becomes uneven depending on light distribution of the solid-state light emitting elements or distance between the solid-state light emitting elements to thereby give rise to luminance unevenness. Also, a distribution of incident angles on respective sites of the fluorescent substance layer becomes uneven to further give rise to color unevenness.
A second problem is that the fluorescent substance layer generally has a plate-like shape, so that a component of which an incident angle from the solid-state light emitting elements onto the fluorescent substance layer is large is easily reflected, and therefore light extraction efficiency is reduced.
Also, positions where the LEDs are mounted on the board and amounts of the translucent resin layer that seals the LEDs may generally be uneven among the plurality of LEDs, and therefore distances between the LEDs and the wavelength converting member become uneven. Luminance and color of the light emitted from the surface of the wavelength converting member vary depending on a position on the surface, and therefore luminance unevenness and color unevenness may occur.